FIG. 1 is a cross-sectional view of a conventional monolithic IC interconnect architecture. Monolithic ICs generally comprise a number passive and/or active devices, such as metal-oxide-semiconductor field-effect transistors (MOSFETs), or the like, fabricated over a substrate 101. These devices are monolithically integrated by levels of metal interconnects embedded within layers of dielectric materials (e.g., 105 and 115) providing electrical isolation. With device dimensions scaling down from one technology generation to the next, it is desirable to also scale down interconnect metal line size and the spacing CDs between adjacent interconnect lines 110 and 111. However, as dimensions of interconnects scale down, the minimum distance between lines intended to be electrically isolated has decreased very rapidly. This is because the decrease in minimum distance is not only a result of the scaling of the interconnect line spacing CDs, but is also a function of registration error that has generally not improved in pace with dimensional shrinks at each technology generation.
For example, in FIG. 1 the minimum distance S1 between interconnect wires is determined by the spacing between an upper interconnect level via 121, designed to land on lower level metal line 111, and the adjacent lower level metal wire 110, which is spaced apart from line 111 by a minimum design spacing CDs. The registration error or misregistration between interconnect levels (e.g., between via 121 and the lower-level metal lines 110, 111) uncontrollably reduces the minimum design spacing CDs to S1. Furthermore, as line spacing continues to decrease, line edge roughness becomes a more significant fraction of CDs, increasing susceptibility to time-zero shorts, and to time dependent dielectric breakdown (TDDB) fails during IC device usage.
Because shorts and TDDB fails negatively impact IC device yield and/or device reliability, interconnect architectures that offer greater scalability through increased shorting margin and improved reliability are advantageous.